Overlap and specificity of genetic and environmental influences on excessive acquisition and difficulties discarding possessions: Implications for hoarding disorder.

A reluctance to discard items, leading to severely cluttered living spaces, is the landmark feature of hoarding disorder (HD). Many, but not all, individuals with HD also excessively acquire, buy or even steal items that they do not need and for which no space is available. In DSM-5, "excessive acquisition" can be coded as a specifier of HD. Despite their consistent co-occurrence, the question of whether excessive acquisition and difficulties discarding possessions share a common etiology remains unanswered. The current study sought to flesh out this relationship by examining the extent of shared genetic and environmental influences on the association between excessive acquisition and difficulties discarding in a community sample of adult, female twins. A total of 5,022 female twins (2,529 pairs; mean age = 55.5 years) completed a self-report measure of hoarding symptoms, including items assessing excessive acquisition and difficulties discarding. The data were analyzed using bivariate twin modeling methods in the statistical program Mx. As expected, we found a strong phenotypic correlation (0.63) between excessive acquisition and difficulty discarding items. Both traits were moderately heritable. The genetic correlation between the traits was estimated to be 0.77 (95% CI: 0.69-0.85), indicating a substantial but imperfect genetic overlap. The non-shared environmental correlation (0.50 [95% CI: 0.42-0.57]), though lower, was also significant. The findings demonstrate a substantial genetic, and more modest environmental, etiological overlap between the excessive acquisition of possessions and difficulties discarding them, providing a possible explanation for their frequent co-occurrence in HD. However, given that the etiological overlap is not perfect, unique etiological influences, particularly environmental, on each phenotype seem plausible.

Evidence for a genetic overlap between body dysmorphic concerns and obsessive-compulsive symptoms in an adult female community twin sample.

Body dysmorphic disorder (BDD) is thought to be etiologically related to obsessive-compulsive disorder (OCD) but the available evidence is incomplete. The current study examined the genetic and environmental sources of covariance between body dysmorphic and obsessive-compulsive symptoms in a community sample of adult twins. A total of 2,148 female twins (1,074 pairs) completed valid and reliable measures of body dysmorphic concerns and obsessive-compulsive symptoms. The data were analyzed using bivariate twin modeling methods and the statistical programme Mx. In the best-fitting model, the covariation between body dysmorphic and obsessive-compulsive traits was largely accounted for by genetic influences common to both phenotypes (64%; 95% CI: 0.50-0.80). This genetic overlap was even higher when specific obsessive-compulsive symptom dimensions were considered, with up to 82% of the phenotypic correlation between the obsessing and symmetry/ordering symptom dimensions and dysmorphic concerns being attributable to common genetic factors. Unique environmental factors, although influencing these traits individually, did not substantially contribute to their covariation. The results remained unchanged when excluding individuals reporting an objective medical condition/injury accounting for their concern in physical appearance. The association between body dysmorphic concerns and obsessive-compulsive symptoms is largely explained by shared genetic factors. Environmental risk factors were largely unique to each phenotype. These results support current recommendations to group BDD together with OCD in the same DSM-5 chapter, although comparison with other phenotypes such as somatoform disorders and social phobia is needed.

Seemingly minor changes to a questionnaire can make a big difference to mean scores: a cautionary tale.

BACKGROUND: It is not unusual for researchers to make apparently minor modifications to existing instruments without checking if this alters psychometric properties. METHOD: Equivalent items on child mental health from two different versions of the Rutter parent questionnaire were compared: items from the standard version and from a modified version. The parents of 400 children aged 5-7 years were randomised into two groups: each group completed one version of the Rutter as well as an independent measure of psychopathology (the Strengths and Difficulties Questionnaire; SDQ). RESULTS: The mean psychopathology scores of the two groups were comparable according to the SDQ but differed markedly between the two Rutter versions, principally because of changes in the response categories. Nevertheless, the validity of the two versions of the Rutter was similar as judged from Rutter-SDQ correlations. CONCLUSION: Seemingly minor changes in the wording of a measure can have a major impact on mean scores, thereby making it harder to compare or combine the results of studies using the original and the modified measure.

Masculine girls and feminine boys: genetic and environmental contributions to atypical gender development in early childhood.

In this genetic study of atypical gender role development, parents of 5,799 twin pairs, ages 3 and 4, rated their twin children's masculinity and femininity. Boys were selected as gender atypical if they were highly feminine (top 5%, 10%, or 15%) relative to other boys, and girls were selected if they were highly masculine relative to other girls. Gender-atypical boys and girls were each divided into 2 groups: fully gender atypical (e.g., feminine boys also low on masculinity) and partially gender atypical (e.g., feminine boys who are not low on masculinity). DeFries-Fulker (DF; J. C. DeFries & D. W. Fulker, 1985, 1988) extremes analysis yielded moderate group heritability and substantial shared environment effects for atypical gender role behavior. However, for fully gender-atypical girls, group heritability accounted for most of the variance, and shared environment had no effect. The results are discussed in light of past studies and potential implications for atypical gender development.

Time trends in child and adolescent mental disorders.

PURPOSE OF REVIEW: 1995 saw the publication of a major review of time trends in psychosocial disorders of youth across the second half of the twentieth century. It found evidence for substantial increases in rates of youth crime, alcohol and drug use, depression and suicide in most industrialized countries in the decades following the Second World War, slowing in some instances in the 1980s. Ten years on, we review findings on more recent trends in rates of these and other indicators of child and adolescent mental health. RECENT FINDINGS: Prevalence estimates for autism spectrum disorders have increased in recent decades, as has public and professional awareness of hyperactivity and attention deficits. Trends in adolescent conduct problems, and in alcohol and drug use, appear to reflect culture-specific influences. Rates of suicide among young males, and self-harm among females have risen in many countries in recent years; trends in emotional disorders are more varied, but there is little evidence for any rise in rates of anorexia nervosa. Although some contributors to these trends have been identified, much remains to be learned about the key risks involved. SUMMARY: Monitoring time trends in child and adolescent mental health is essential for service planning; knowledge of changing trends can also provide important pointers to potential risk factors. Current data sources allow relatively reliable tracking of trends in some areas, but remain severely limited in others. Further research is needed to understand the mechanisms underlying recently identified trends in child and adolescent mental health.

Experiential avoidance and emotion regulation difficulties in hoarding disorder.

Experiential avoidance can be defined as the tendency to avoid contact with unwanted internal experiences. Current conceptualizations of pathological hoarding appear broadly consistent with an experiential avoidant model. Eighty participants in four groups, namely hoarding disorder (HD) without comorbid obsessive-compulsive disorder (OCD), HD with comorbid OCD, non-hoarding OCD, and healthy controls, were administered measures of experiential avoidance and emotion regulation difficulties. Hoarding individuals reported higher levels of experiential avoidance and difficulties in emotion regulation compared to healthy but not to OCD participants. Both experiential avoidance and emotion regulation difficulties were significantly more prominent when HD was comorbid with OCD than when HD occurred without comorbid OCD. Correlation analyses further showed that both experiential avoidance and emotion regulation were moderately but significantly associated with obsessive-compulsive but not hoarding symptoms. Thus, experiential avoidance and emotion regulation difficulties are not specifically relevant to HD but to a broad range of psychopathologies. However, despite the lack of specificity, the findings raise some potentially useful clinical implications for the treatment of HD.

Stressful life events and material deprivation in hoarding disorder.

Traumatic life events and early material deprivation have been identified as potential environmental risk factors for the development of pathological hoarding behavior, but the evidence so far is preliminary and confounded by the presence of comorbid obsessive-compulsive disorder (OCD). This study retrospectively examined the occurrence of traumatic/stressful life events and material deprivation in four well-characterized groups: hoarding disorder without comorbid OCD (HD; n=24), hoarding disorder with comorbid OCD (HD+OCD; n=20), OCD without hoarding symptoms (OCD; n=17), and non-clinical controls (Control; n=20). Participants completed clinician and self-administered measures of hoarding, OCD, depression, psychological adjustment, and traumatic experience. Semi-structured interviews were undertaken to assess the temporal relation between traumatic/stressful life events and the onset and worsening of hoarding symptoms, and to determine the level of material deprivation. Although rates of post-traumatic stress disorder were comparable across all three clinical groups, hoarders (regardless of the presence of comorbid OCD) reported greater exposure to a range of traumatic and stressful life events compared to the two non-hoarding groups. Results remained unchanged after controlling for age, gender, education level, depression, and obsessive-compulsive symptoms. The total number of traumatic life events correlated significantly with the severity of hoarding but not of obsessive-compulsive symptoms. About half (52%) of hoarding individuals linked the onset of hoarding difficulties to stressful life circumstances, although this was significantly less common among those reporting early childhood onset of hoarding behavior. There was no link between levels of material deprivation and hoarding. Results support a link between trauma, life stress and hoarding, which may help to inform the conceptualization and treatment of hoarding disorder, but await confirmation in a representative epidemiological sample and using a longitudinal design.

A multivariate twin study of obsessive-compulsive symptom dimensions.

CONTEXT: Obsessive-compulsive disorder (OCD) is clinically heterogeneous, but it is unclear whether this phenotypic heterogeneity reflects distinct, or partially distinct, etiologic mechanisms. OBJECTIVE: To clarify the structure of the genetic and environmental risk factors for the major symptom dimensions of OCD. DESIGN: Self-report questionnaires and multivariate twin model fitting. SETTING: General community. PARTICIPANTS: A total of 4355 female members of the TwinsUK adult twin register. MAIN OUTCOME MEASURES: Scores on the Obsessive-Compulsive Inventory-Revised and 5 of its subscales (checking, hoarding, obsessing, ordering, and washing). RESULTS: A common pathway model did not fit the data well, indicating that no single latent factor can explain the heterogeneity of OCD. The best-fit multivariate twin model was an independent pathway model, whereby both common and unique genetic and/or environmental factors contribute to the etiology of each symptom dimension. The hoarding dimension had the lowest loading on the common factor and was more influenced by specific genetic effects (54.5% specific). With the exception of hoarding, most of the genetic variance was due to shared genetic factors (ranging from 62.5% to 100%), whereas most of the nonshared environmental variance was due to dimension-specific factors. CONCLUSIONS: Obsessive-compulsive disorder is unlikely to be an etiologically homogeneous condition. There is substantial etiologic overlap across the different OC symptom dimensions, but dimension-specific genetic, and particularly nonshared environmental, factors are at least as important. Hoarding shares the least amount of genetic liability with the remaining symptom dimensions. The results have implications for the current deliberations regarding OCD and the inclusion of a putative hoarding disorder in DSM-5.

Prevalence and heritability of compulsive hoarding: a twin study.

OBJECTIVE: Compulsive hoarding is a serious health problem for the sufferers, their families, and the community at large. It appears to be highly prevalent and to run in families. However, this familiality could be due to genetic or environmental factors. This study examined the prevalence and heritability of compulsive hoarding in a large sample of twins. METHOD: A total of 5,022 twins completed a validated measure of compulsive hoarding. The prevalence of severe hoarding was determined using empirically derived cutoffs. Genetic and environmental influences on compulsive hoarding were estimated using liability threshold models, and maximum-likelihood univariate model-fitting analyses were employed to decompose the variance in the liability to compulsive hoarding into additive genetic and shared and nonshared environmental factors (female twins only; N=4,355). RESULTS: A total of 2.3% of twins met criteria for caseness, with significantly higher rates observed for male (4.1%) than for female (2.1%) twins. Model-fitting analyses in female twins showed that genetic factors accounted for approximately 50% of the variance in compulsive hoarding, with nonshared environmental factors and measurement error accounting for the other half. CONCLUSIONS: Compulsive hoarding is highly prevalent and heritable, at least in women, with nonshared environmental factors also likely to play an important role.

Genetic and environmental influences on sex-typed behavior during the preschool years.

The genetic and environmental etiologies of sex-typed behavior were examined during the preschool years in a sample of 3,990 three- to four-year-old twin and non-twin sibling pairs. Results showed moderate genetic and significant shared environmental influence for boys and substantial genetic and moderate shared environmental influence for girls. For both boys and girls, twin-specific shared environmental effects contributed to twins' similarity in gender role behavior and accounted for approximately 22% of the shared environmental variance. These findings extend previous research conducted with older samples by showing not only important genetic contributions to gender role behavior but also an important role for shared environment. The inclusion of non-twin siblings showed that some of the shared environmental influence is specific to twins.

Genetic and environmental influences in adolescent peer socialization: evidence from two genetically sensitive designs.

Harris argues that peer relationships are the chief determinants of personality development. Harris's thesis makes the behavioral genetic investigation of peer groups particularly timely. The present study examined genetic and environmental contribution to self-reported peer-group characteristics in two samples of adolescent siblings: 180 adoptive and nonadoptive sibling pairs from the Colorado Adoption Project, and 386 sibling pairs from the Nonshared Environment and Adolescent Development Study. Substantial genetic influence emerged for college orientation, with the remaining variance accounted for by nonshared environment. For delinquency, however, the majority of the variance was explained by nonshared environment. Although genetic influence was implicated for peer popularity in twin analyses, genetic factors were not important in explaining individual differences in nontwin siblings. These results suggest that although some dimensions of peers are somewhat mediated by genetic factors, nonshared environmental influence is substantial.